Phase change material heat sink

ABSTRACT

A phase change material heat sink includes a sealed enclosure containing a phase change material. A fluid passage element is in contact with the sealed enclosure and includes a thermal exchange layer in thermal contact with the top and that directs fluid in a first flow direction and a shunt passage element in thermal contact with at least one of the sides or the bottom and that directs fluid in a second flow direction.

FIELD OF INVENTION

The subject matter disclosed herein relates generally to the field ofheat sinks and, in particular, to phase change material heat sinks

DESCRIPTION OF RELATED ART

Phase change material (PCM) heat sinks utilize PCM's such as water, wax,or other materials with desirable melting points to store and releaseheat energy associated with the solid-liquid phase change. The energyassociated with such a change is generally referred to as the latentheat of fusion. One type of PCM heat sink uses a heat transport fluid tocarry thermal energy into and out of the heat sink. The fluid flowsthrough a fluid passage element that bring the fluid into thermalcontact with the PCM to allow heat transfer to occur while keeping thefluid isolated from the PCM.

BRIEF SUMMARY

According to one embodiment, a phase change material heat sink includesa sealed enclosure containing a phase change material and that includesa top, a bottom and sides. The phase change material heat sink of thisembodiment further includes a fluid passage element in contact with thesealed enclosure that includes a thermal exchange layer in thermalcontact with the top and that directs fluid in a first flow directionand a shunt passage element in thermal contact with at least one of thesides or the bottom and that directs fluid in a second flow direction.In this embodiment, the fluid passage element is configured to directthe fluid through the shunt passage element before it is directed to thethermal exchange layer.

According to another embodiment, a phase change material heat sinkincludes a sealed enclosure containing a phase change material andincluding a top, a bottom and sides. The phase change material heat sinkof this embodiment also includes a fluid passage element in contact withthe sealed enclosure, the fluid passage element including a thermalexchange layer in thermal contact with the top and that directs fluid ina first flow direction and a shunt passage element passing between thetop and bottom that directs fluid in a second flow direction. In thisembodiment, the fluid passage element is configured to direct the fluidthrough the shunt passage element before it is directed to the thermalexchange layer.

According to yet another embodiment a phase change material heat sinkincludes a sealed enclosure containing a phase change material andincluding outer walls. The phase change material heat sink of thisembodiment also includes a fluid passage element in contact with theouter walls, the fluid passage element including a thermal exchangelayer in thermal contact with one side of the outer walls that directsfluid in a first flow direction and a shunt passage element in thermalcontact with another side of the outer walls that directs fluid in asecond flow direction. In this embodiment, the fluid passage element isconfigured to direct the fluid through the shunt passage element beforeit is directed to the thermal exchange layer.

Other aspects, features, and techniques of the invention will becomemore apparent from the following description taken in conjunction withthe drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Referring now to the drawings wherein like elements are numbered alikein the several FIGURES:

FIG. 1 is an exploded view of a phase change material heat sinkaccording to the prior art to illustrate short comings thereofrecognized and solved, or reduced, by embodiments of the presentinvention;

FIG. 2 is an exploded view of the a phase change material heat sinkaccording to one embodiment of the present invention; and

FIG. 3 is an exploded view of a phase change material heat sinkaccording to another embodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a prior art PCM heat sink 100 in an exploded view.The PCM heat sink 100 includes a sealed PCM containing chamber 106. Thissealed chamber 106 includes a PCM material 120 such as water or waxsealed therein. The sealed chamber 106 includes a top 107 and a bottom108. In FIG. 1, the sealed chamber 106 is illustrated such that the PCMmaterial 120 is visible. However, it shall be understood that inpractice, the top 107 is formed of solid material and that the PCMmaterial 120 may not be not visible.

The PCM heat sink 100 also includes a fluid passage element 101. A heattransmission fluid enters (e.g., Freon or water, for example) an end 103of the fluid passage element 101 via inlet passage (e.g., pipe) 102 andexits it via outlet passage 114. The fluid generally traverses the fluidpassage element 102 in the direction shown by arrow A. The fluid passageelement 101 illustrated in FIG. 1 includes a connector portion 104arranged between the ends 103 through which the fluid passes whiletraversing from the inlet passage 102 to the outlet passage 114. Theconnector portion 104 in particular, and the fluid passage element 101generally, includes a bottom 105. When the PCM heat sink 100 isassembled, the top 107 of the sealed chamber 106 is in thermal contactwith the bottom 105 of the fluid passage element 101.

The PCM heat sink 100 also optionally include a heat release element111. As illustrated, the heat release element 111 includes heatdiffusion fins 113 and a top 112. In some cases, the heat releaseelement 111 can be brought into thermal contact with the sealed chamber106 to dissipate heat stored therein. For example, in the context of asatellite, heat may be stored in the sealed chamber 106 until thesatellite is not in line-of-sight with the sun. At that time, the bottom108 of the sealed chamber 106 can be brought into contact with the top112 of the heat release element 111 and the heat can be released viafins 113 into space.

A problematic aspect of a PCM heat sink such as that illustrated in FIG.1 is that phase change materials expand or contract during phasechanges. Expansion due to phase changes can create significant pressureincreases within the sealed enclosure 106. To further explain the priorsolutions and the shortcomings thereof, the top 107 of the sealedenclosure 106 is illustrated as being transparent and containing a PCM120. To provide room for thermal expansion, a void space 110 may be leftwithin the enclosure 106 to account for the volume change. In somecases, however, the liquid state (e.g., expanded) PCM can be physicallyblocked by solid PCM from reaching the void space 110. For example,assuming that fluid is flowing in direction A in FIG. 1, the PCM 120changes to a liquid phase in a liquid region 109. This liquid region 109is not in contact with the void 110. As such, the pressure in the liquidregion 109 will increase.

The prior art has proposed several different solutions to the aboveproblem. One is to utilize a movable accumulator to account for thevolume change. Another approach is to contain the pressure within astructure that can withstand the forces that develop. Yet anotherapproach is to immobilize the PCM in a substrate, such as a fiber orfoam structure. When the PCM is immobilized, the void spaces becomeevenly distributed within the chamber 106 so that there is no volumechange on the macroscopic scale. This eliminates the high pressures thatcan develop within the chamber 106. However, such an approach addscomplexity to the manufacturing approach and, also, limits processingthat can be performed on the enclosure 106 itself.

FIG. 2 illustrates a PCM heat sink 200 according to one embodiment ofthe present invention. In this embodiment, the heat sink 200 includessealed enclosure 206 that can be the same as or similar to the sealedenclosure 106 that is illustrated in FIG. 1.

The sealed enclosure 206 is formed at least partially of metal in oneembodiment and can optionally be braised. While not illustrated, itshall be understood that the embodiments shown in FIGS. 2 and 3 can bothinclude a heat release element as is generally described above but it isnot required.

As illustrated, the sealed enclosure 206 includes a PCM 120 and isformed such that a void space 110 exists therein. In FIG. 2, the top 207of the sealed enclosure 206 is shown as being clear but it will berealized that this is for explanation only. The exact configuration ofthe sealed enclosure 206 can vary from that illustrated in FIG. 2. Forexample, the sealed enclosure 206 could be circular in shape or couldtake on any other geometric shape. As illustrated, the sealed enclosure206 includes sides 230. It shall be understood that the sealed chamber206 can include one or more internally located fins formed of foam ormetal that extend inwardly from the sides 230 or top 207 thereof intothe PCM material 120.

In this embodiment, the PCM heat sink 200 also includes a fluid passageelement 201. The fluid passage element 201 includes a thermal exchangelayer 222 and one or more shunt passage elements 202. Generally, thethermal exchange layer 222 directs fluid from a first end 226 to asecond end 228. As the fluid passes through the fluid passage element201, a bottom side 229 thereof allows heat to be transferred between thefluid and the top 207 of the sealed enclosure 206 to transfer heatto/from the liquid from/to the PCM 120.

In contrast to the prior art, the fluid passage element 201 causes fluidto be directed in a first direction (arrow A) and a second direction(shown by arrow B) that is different than the first direction. In oneembodiment, the first and second directions represent counter-flowdirections. In a particular embodiment, the first and second directionsare anti-parallel to one another. The counter-flow arrangement, asexplained further below, causes shunt passages 204 of liquid PCM to becreated in the PCM to allow liquid phase PCM 109 to reach and flow intothe void space 110 regardless of the location of the void space 110.

In one embodiment, the shunt passage elements 202 (e.g, pipes) are inthermal contact with the sides 230 of the enclosure 206. In oneembodiment, the shunt passage elements 202 could be repositioned tocontact a bottom 232 of the enclosure 206. A fluid is received into thefluid passage elements 202 that is travelling in the direction B. Theheat of that fluid causes shunt passages 204 of liquid PCM to form inthe PCM.

As illustrated, two shunt passage elements 202 are provided. Of course,any number of shunt passage elements greater than or equal to one couldbe included. Regardless, the fluid passing through the shunt passageelements 202 is collected in and redirected an end 205 of the shuntpassage elements 202. At end 205, the fluid is transferred into thefirst end 226 of the thermal exchange layer 222 and then travels indirection A towards the second end 228 of the thermal exchange layer222. Generally, the change of direction is shown by linking direction Cwhere the fluid flow direction translates from direction B to directionA but, as one of ordinary skill will realize, other end configurationsand direction reversal mechanisms could be employed than thoseillustrated in FIG. 2.

FIG. 3 illustrates another embodiment of a PCM heat sink 300. Thisembodiment includes a sealed PCM enclosure 302 configured for thermalcontact with a fluid passage element 304 that includes a thermaltransfer layer 322 and shunt passage elements 306. The flows of a fluidthrough thermal transfer layer 322 and shunt passage elements 306 arecounter to one another as described above with respect to FIG. 2. Inthis embodiment, rather than passing along the sides of the sealedenclosure 302, shunt passage elements 306 pass through the sealedenclosure 302. The fluid traveling in direction B thereby melts PCM inthe enclosure 302 that surrounds them to provide passages between aliquid portion of the PCM and a void space regardless of the location ofthe void space.

It shall be understood that, while not illustrated, the sealed enclosure302 could be cylindrical in shape. In such a case, the shunt passageelements 306 can be located on an external wall of the cylinder and thethermal transfer layer 322 can be located on an internal wall of thecylinder or vice versa. Operation of such an embodiment can be the sameor similar to that as described above.

The technical effects and benefits of exemplary embodiments includeproviding a mechanism to create fluid expansion channels in a PCM heatsink to reduce or eliminate harmful effects of thermal expansion.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention.While the description of the present invention has been presented forpurposes of illustration and description, it is not intended to beexhaustive or limited to the invention in the form disclosed. Manymodifications, variations, alterations, substitutions, or equivalentarrangement not hereto described will be apparent to those of ordinaryskill in the art without departing from the scope and spirit of theinvention. Additionally, while various embodiment of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims.

1. A phase change material heat sink comprising: a sealed enclosurecontaining a phase change material and including a top, a bottom andsides; and a fluid passage element in contact with the sealed enclosure,the fluid passage element including a thermal exchange layer in thermalcontact with the top and that directs fluid in a first flow directionand a shunt passage element in thermal contact with at least one of thesides or the bottom and that directs fluid in a second flow direction,wherein the fluid passage element is configured to direct the fluidthrough the shunt passage element before it is directed to the thermalexchange layer.
 2. The phase change material heat sink of claim 1,wherein the sealed enclosure is formed at least partially of metal. 3.The phase change material heat sink of claim 3, wherein the sealedenclosure is formed of braised metal.
 4. The phase change material heatsink of claim 1, wherein the phase change material is wax.
 5. The phasechange material heat sink of claim 1, wherein the shunt passage elementincludes a first element and a second element, the first element beingin contact with a first of the sides and the second element being incontact with a second of the sides.
 6. The phase change material heatsink of claim 1, wherein the first flow direction is anti-parallel tothe second direction.
 7. The phase change material heat sink of claim 1,wherein the shunt passage element is in thermal contact with at leastone of the sides and further comprising: a heat release element inthermal contact with the bottom or the sides of the sealed enclosure. 8.A phase change material heat sink comprising: a sealed enclosurecontaining a phase change material and including a top, a bottom andsides; and a fluid passage element in contact with the sealed enclosure,the fluid passage element including a thermal exchange layer in thermalcontact with the top and that directs fluid in a first flow directionand a shunt passage element passing between the top and bottom thatdirects fluid in a second flow direction, wherein the fluid passageelement is configured to direct the fluid through the shunt passageelement before it is directed to the thermal exchange layer.
 9. Thephase change material heat sink of claim 8, wherein the sealed enclosureis formed of a metal.
 10. The phase change material heat sink of claim9, wherein the sealed enclosure is formed of braised metal.
 13. Thephase change material heat sink of claim 8, wherein the phase changematerial is wax.
 14. The phase change material heat sink of claim 8,wherein the first flow direction is anti-parallel to the seconddirection.
 15. The phase change material heat sink of claim 8, furthercomprising: a heat release element in thermal contact with the bottom ofthe sealed enclosure.
 16. A phase change material heat sink comprising:a sealed enclosure containing a phase change material and includingouter walls; and a fluid passage element in contact with the outerwalls, the fluid passage element including a thermal exchange layer inthermal contact with one side of the outer walls that directs fluid in afirst flow direction and a shunt passage element in thermal contact withanother side of outer walls that directs fluid in a second flowdirection, wherein the fluid passage element is configured to direct thefluid through the shunt passage element before it is directed to thethermal exchange layer.